The dual fluid heat engine has been described in U.S. Pat. Nos. 3,978,661, 4,128,994 and 4,248,039. Parameter optimization and control paths for the dual fluid heat engine are described in U.S. Pat. Nos. 4,297,841, 4,417,438 and 4,393,649. This invention relates to an apparatus for the removal of noncondensable gases from process steam cogenerated during operation of the Cheng cycle engine.